Proliferation and differentiation are important processes within the ovaries and testes. Uncontrolled proliferation results in cancer whereas failure to differentiate can result in infertility. Cell cycle regulators and TGF(3 superfamily signaling pathways play key roles in both processes. Cyclin D2 null mice have decreased granulosa cell proliferation and smaller testes whereas p27 null mice have increased Sertoli cell proliferation and defects in granulosa cell terminal differentiation. With the support of this grant, we have shown that the inhibins, a:p members of the TGFp superfamily, function in the gonads as tumor suppressors and that cyclin D2/inhibin a double mutants have slowed tumor development whereas p27/inhibin a double mutants die of gonadal tumors very rapidly. Both gonadotropins (FSH and LH) are also involved in the tumorigenesis process. Given the emerging relationship between cyclin D2, FSH, and the retinoblastoma (RB) tumor suppressor in granulosa cells and consistent with findings that the RB pathway is deregulated in most human cancers, our working model is that RB is central to the development of these ovarian and testicular cancers. Our overall hypothesis is that the inhibin/activin/BMP, RB/E2F, FSH, LH, and cell cycle pathways converge to regulate the G1 to S phase transition and that modulation of the activity (phosphorylation) state of RB by cell cycle regulators (e.g., cyclin D2/CDK4, cyclin E2(E1)/CDK2, and p27) and inhibin determines the proliferation and terminal differentiation of granulosa or Sertoli cells, ultimately affecting the predisposition of these cells to cancer. The Specific Aims of the proposed studies are: 1) Define the physiologic roles of the retinoblastoma (RB) tumor suppressor in granulosa cell and Sertoli cell proliferation and differentiation; 2) Determine if the RB protein is a genetic modifier of tumor development in the inhibin a knockout model; 3) Establish the relative roles of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in granulosa cell and Sertoli cell proliferation, differentiation, and tumor development; and 4) Characterize the alterations in cell cycle regulation, cell adhesion, and responsiveness to LH that occur early in the transformation of granulosa cells into cancer. Characterization of these mice will lead to important insights into the development of gonadal cancers in men and women and the roles of several proteins in reproductive physiology.